1. Technical Field
The present invention relates to a rubber composition suitable for use in a tire tread, a method for producing the rubber composition, a pneumatic tire using the rubber composition, and a method for manufacturing the pneumatic tire.
2. Related Art
Various technologies are proposed in a tread rubber of a pneumatic tire in order to improve running performance on an ice-covered road surface (that is, on-ice performance) and running performance on a wet road surface (that is, wet performance). For example, JP-A-2015-059169 discloses adding an acid-treated silk powder to a tread rubber in order to improve on-ice performance. Further technical development for improving running performance of a tire is required in order to sufficiently respond to a market demand.
Oil that is a petroleum softener is generally added to a tread rubber. The oil migrates with time (bleeding to a rubber surface or migration to surrounding rubbers). Therefore, there is a problem that rubber hardness of a tread rubber increases by the migration of oil, and this causes deterioration of tire performance after passing of years.
JP-A-H01-163228 proposes adding an oil gelling agent (for example, N-lauroyl-L-glutamic acid-α,γ-di-n-butylamide) to an age resister in order to improve ozone crack resistance by an age resister. However, this patent document discloses that an age resister is gelled by an oil gelling agent, and does not disclose use of oil absorptive polymer particles and suppression of hardness increase by migration of an oil.